Comprehensive rehabilitation programs which include some form of exercise reconditioning have had considerable success in improving exercise capacity, psychological status and even medical outcome in patients with chronic obstructive lung disease. Uncertainty about the methods by which exercise training can be most effectively performed has limited broad implementation of rehabilitation programs. The present study is designed to examine, within the context of a comprehensive rehabilitation program, the relative effectiveness of specific respiratory muscle training and general body exercise on respiratory muscle strength and endurance; exercise capacity; psychologic function; and medical outcome. Specific respiratory muscle training will be performed by breathing against a hand held resistor. General body exercise will be performed on a bicycle ergometer. Both types of training will be performed under laboratory supervision four times a week for a one year period. Since anxiety associated with dyspnea may interfere with exercise training, the effectiveness of a program of biofeedback controlled desensitization of the anxiety developing during exercise on patient acceptance of the training regimen will be assessed. Respiratory muscle strength will be examined from the maximal static inspiratory and expiratory pressure generated over a range of lung volumes. Muscle endurance will be assessed from the time to exhaustion breathing against inspiratory threshold loads and from the rate of change of the power spectral density of the surface recorded EMG of the diaphragm. Exercise capacity will be assessed from: the maximal oxygen consumption during a progressive incremental work test; the endurance time during submaximal exercise; and the distance walked in the 12 minute walk test. Psycho-social function will be assessed using standard objective questionnaires. Nutritional status will be assessed anthropomorphically and biochemically. Medical outcome will be assessed from the days lost from work or spent in hospital and mortality rate. In addition to training, subjects will be provided with a comprehensive program of medical care, instruction in smoking cessation and proper nutrition, and psychological counselling to improve coping skills. Subjects will be re-evaluated at 3 months, 6 months, and 1 year after initiating rehabilitation and annually thereafter. The results of this study should provide important information about the mechanisms underlying the favorable responses previously observed in exercise rehabilitation programs and so should help in the design of future rehabilitation efforts.